1. Field of the Invention
The present invention relates to vibration suppressors and more particularly to an active suppressor for supressing vibrations in structures such as buildings.
2. Description of the Prior Art
The use of passive and active vibration dampeners for controlling vibrations is well known in the art. In a passive vibration dampening system, it is common to utilize a seismic mass coupled to the structure by a spring in parallel with a damper. However, in this type of suppressor, the disturbing frequency must be very nearly constant if the effective mass is to be kept small. When the disturbing frequency is not constant, additional mass must be added which may be essentially equal to the structural mass. There have been a number of approaches to vibration suppression using active elements that have proved suitable for control of the vibration of flexible bodies. For example, in U.S. Pat. No. 3,566,993 to Leatherwood et al, an amplified active system is disclosed. The system moves the housing of a device, flexibly attached to the housing, in a direction opposite to a sensed movement of the device. However, this approach is not suitable for a structure such as a building. Hehl et al in U.S. Pat. No. 4,101,009 teach absorbing oscillations between a frame and a continuously oscillating mass by making the mass system and its drive means operate in a manner to produce out of phase motion of the frame and the mass. Other U.S. patents concerned with vibration suppression or absorption include U.S. Pat. No. 3,917,246 to Gartner et al; U.S. Pat. No. 2,777,544 to O'Connor; and U.S. Pat. No. 3,483,951 to Bonesho et al. However, none of these approaches are suitable to suppress vibrations in commercial buildings.
In the design of commercial buildings, it is apparently very difficult for the design architects and engineers to foresee vibration problems. In buildings in which heavy vehicles are required to operate, it is found that the movements of such vehicles produce very disturbing vibrations throughout floors, walls, and ceilings of the buildings. In the past, the approach to reducing building and structural vibration has been to alter the structure or to add additional structural elements such as posts, columns, and the like, all of which are expensive and may interfere with the use of the building. Therefore, there is a need for an active vibration suppression means which can be added to an existing building without significant structural alterations thereto.